There is a desire in the aerospace industry to move towards gas turbine engines which reduce the amount of NOx emissions. In order to achieve this, lean burn combustion processes are required, so as to limit the flame temperature in the combustor, and hence limit NOx production. In order to achieve these reduced temperatures, most of the combustion air has to be burnt in the combustor, with little remaining for cooling the combustor walls.
The fuel injectors required for such lean burn combustors are larger than the injectors for conventional combustors. As a result, the conventional diffuser for feeding the air from the compressor to the combustor is inadequate.